Signals may be used to transmit data over distances from a transmitter to a receiver. In optical communication systems, for example, data may be modulated on one or more optical wavelengths to produce modulated optical signals that may be transmitted over optical waveguides or paths such as optical fibers. Optical communications systems have used techniques, such as wavelength division multiplexing (WDM), to increase the transmission capacity. In a WDM system, a plurality of optical channels may be established based on a plurality of corresponding optical carrier wavelengths with multiple signals modulated on the separate channel wavelengths and combined to form an aggregate multiplexed signal or WDM signal. Modern WDM systems have a high traffic capacity, for example, a capacity to carry 96 or more channels at 10 gigabits per second (hereinafter Gb/s) or more.
A WDM system may include a relatively long trunk path (e.g., optical fiber) that may be terminated at a transmitting and/or receiving trunk terminal. Some WDM systems, such as branched undersea networks, may further include one or more branching units situated along the trunk path. Each branching unit (BU) may be connected to a branch path (e.g., optical fiber) that terminates in a transmitting and/or receiving branch terminal. Each BU may include one or more optical add/drop multiplexers (OADM). Channels may be dropped from and/or added to the trunk path via the OADMs to direct optical signals on selected channels to and from the branch terminals.
Security concerns are often encountered in optical communication systems as a result of optical signals including data traffic being directed to a terminal that was not intended to receive the data traffic. In branched undersea networks, for example, the added flexibility provided by OADMs may result in potential security concerns. OADMs allow system operators new levels of flexibility in sharing the capacity on a single fiber pair among multiple point-to-point connections in a branched network. This capability may improve the cost effectiveness of bandwidth delivery, especially to landing points with modest capacity requirements. Using OADMs in an undersea environment, however, also presents unique challenges and design constraints. In particular, the interdependence between trunk and branch traffic in such systems presents concerns in the event of a fault condition. A fault on a branch path, for example, may impair traffic on a trunk path due to the lack of uniform channel loading, and vice versa.
Some OADM systems in an undersea environment may use a recover mechanism whereby traffic is redirected and used to maintain uniform channel loading during a fault. One example of such a system configured for fault tolerance is disclosed in greater detail in U.S. patent application Ser. No. 12/707,604 filed Feb. 17, 2010, which is commonly owned and fully incorporated herein by reference. Although this solution provides fault tolerance and maintains substantially uniform channel loading, such systems present privacy and security concerns because customer traffic may be redirected to a new, unintended destination during a fault. Similar security and privacy concerns may also arise in point-to-point optical communication systems.